An exhaust sensor is arranged, for example, in an engine exhaust pipe downstream of an exhaust gas post-treatment apparatus in terms of flow of exhaust gas to measure exhaust gas components. The exhaust gas post-treatment apparatus may be, for example, a diesel particulate filter (DPF) for collecting particulate matters (PM) contained in the exhaust gas, and the exhaust sensor may be, for example, a PM sensor for detecting an emission of particulate matters (PM).
One prior art document is WO2009/109688.